Pulse generating circuit utilizing avalanche transistors and tunnel diodes



J. G. DlLL Jan. 22, 1963 3,075,092 PULSE GENERATING CIRCUIT UTILIZING AVALANCHE TRANSISTORS AND TUNNEL DIODES 2 Sheets-Sheet 1 Filed Nov. 22, 1960 J. Gr DlLL Jan. 22, 1963 PULSE vGENEIRATING 3,075,092 CIRCUIT UTILIZING AVALANCHE TRANSISTORS AND TUNNEL DIODES 2 Sheets-Sheet 2 Filed Nov. 22, 1960 RANRAQ United States Patent Oiiiice Filed Nov. 22, 1960, Ser. No. 70,952 6 Claims. (Cl. 307-885) This invention relates to pulse generators and particularly Ito a pulse generating circuit utilizing transistors and negative resistance devices .to develop high power pulses at a high repetition ra-te.

Pulse generators utilizing transistors with an avalanche characteristics have the advantage of providing a simplitied semiconductor circuit that develops very narrow pulses having a relatively large power capability. A .puise generator circuit utilizing avalanche transistors conventionally requires a storage capacitor coupled in the load current path for limiting the peak current during avalanche multiplication so as t prevent damage to the transistor. In the conventional arrangement, the transistor is biased to an avalanche operating point by a power supply-and biasing resistor coupled respectively in series to a point betweenthe capacitor and the load current circuit of the transistor. The capacitor recharges after the formation of each output pulse by current owing through the biasing resistor from the power supply. However, the pulse repetition rate of the generator is greatly limited lby the recovery time provided by the RC time constant of the circuit. Because the operating characteristics of the transistor require that la minimum steady state current be supplied to the transistor and that the potential at the operating point. be maintained Asubstantially const-ant, the valve of the biasing resistor is necessarily relatively large. Thus, the long recovery time required while the storage capacitor is charged through the biasing resistor greatly limits the pulse repetition rate of conventional pulse generator circuits.

It is therefore an object of this invention to provide a high repetition rate pulse generator utilizing semiconductor elements.

It is a further object of this invention to provide a pulse generator utilizing avalanche transistors and operating at a very high repetition rate.

it is a still fur-ther object of this invention to provide a high repetition rate pulse generator having a plurality of stages and utilizing tunnel diodes as logical elements so succeeding stages are sequentially energized to allow recovery time for the preceding stages.

It is another object of this invention to provide an improved arrangement for emitter-triggering an avalanche transistor.

Brieiiy, the circuit in accordance with thi-s invention is a pulse generator including a plurality of sequentially operating pulse generating stages controlled by logical circuitry and connected in parallel through an OR gate to a load. Each stage includes an -avalanche transistor having a first electrode coupled both to the OR gate through a storage means and to a source of charging current and having a second electrode coupled to logical circuitry to which trigger pulses are applied. The logical circuitry in each stage includes iirst and second tunnel diodes coupled to the second electrode of the avalanche transistor, the -second tunnel diode providing potential states to maintain the iirst diode in either a ready low voltage state in a single one of the stages or in a normal low voltage state in the remaining stages. When a trigger pulse is applied to the first tunnel diode of the one stage in which the first tunnel diode is in the ready state, that diode changes to a high voltage state to initiate the transistor into conduction and to develop an output circuit pulse.

ond tunnel diode T21 3,075,092 Patented Jan. 22, 1963 Load current iiowing to the first and second tunnel diodes in that stage then causes the first diode to be set and maintained at the normal low voltage state. The `storage means of each stage is coupled to the second diode of each succeeding stage to set, in the succeeding stage, that diode and in turn the first tunnel diode to the ready state `only after the preceding stage iires` Thus, each stage is successively iired allowing recovery time for the preceding stages so that load pulses may be developed at a high repetition rate.

The novel features `of this invention, as well as the invention itself, both as -to its organization and method of operation, will best be understood from the accompanying description, when in connection with the accompanying drawings, in which:

FIG. 1 is a schematic circuit diagram of the pulse genenating circuit in accordance with this invention;

FIG. 2 is a graph of voltage versus current showing the operating characteristics of the avalanche transistors of FIG. 1; and

FIG. 3 is a graph of voltage versus time showing Waveforms for explaining the sequential operation of the cir cuit in accordance with this invention.

Referring iirst to FIG. l, the pulse generating circuit in accordance with -this invention includes a plurali-ty'of stages, such as stages l, 2 and n, responsive through a lead l0 to `a train of input signal pulses, as shown by a rm` 13, from a trigger pulse source 12 to apply output signal pulses having the characteristic shown by a waveform 14, through a common lead 15 to a common load element as shown 19 is coupled in parallel with the load 13 to suppress positive overshoot voltages of the output signal. Each.` l, 2 and l1 have similar elements so that.

of the stages only the arrangement of the elements of stage l will be described in detail. n

Stage l, for example, includes an avalanche transistor l20 of the n-p-n type with the base through a current limiting resistor 22. As will be explained in further detail subsequently, the avalanche a potential with region thereof, the lead 30 is coupled through a current limiting resistor 44 to a source of positive potential 46, which may be at +200 volts. A second plate 48 of the output lead l5. The diode 52 52b, which may be conventional diodes, form an OR gate so that only the stage forming a pulse of the waveform 14 conducts current to the load 18. The diodes of the OR gate such as 52 are preferably of a type that develops y a small voltage drop in the conductive region.

The logical control circuitry in accordance with this Iinvention coupled to the emitter of the transistor 20,

for example, includes a iirst tunnel diode T11 having a cathode coupled through a lead 56 to the emitter of the transistor Ztl and an anode coupled to ground. A secas a load resistor i8. A diode.

coupled to ground 5 potential may be i the order of 10 volts. The ter-- capacitor 36 and t the capacitors 36 and 42, and for biasing the transistor 20 in the avalanchev and diodes 52a andk has a cathode coupled to a lead 58, which in turn isrcoupled through a resistor 6l) to a lead 62 which is coupled to the emitter of the transistor 2i). The anode of the diode T21 is coupled to a lead` 6,4 which in turn is coupled throu-gh a resistor 6(A to ground. Trigger pulsesfof the waveform 13 are' appliedl through the lead 10V anda coupling resistor 68` to the lead 62. For developing a pulse to be applied to the succeeding stage such'as stage 2 aftera pulse has been formed by the transistor 20 of stage l, alead 74 is Coupled lbetween a plate '76 of the control capacitor 42v to the lead 64 with the. lead 74 coupled to stage 2 by aV lead 84. The cathode of the-diode T21 is biased from a source ofl negative potential 78, which may be at l0 volts, coupled through a biasing resistor 80 to a lead 32 which in4 turn is coupled to .the lead 5S. In orderY that the stage l be set for the ready state by the precedingstage, the-lead S2 is coupled through an isolating resistor 86 vto a lead 84h, which inturn is coupled to the lead74c of stage n.

' Other stages in. accordancewiththis invention, such asstage andstage nwhichare similar to stage l, are indicated by similar numbers with theV addition-of b, andwillv not be explained in further detail. lt is to be noted that, although only. three-stages are shown for conveniencev of. illustration, a greater number mayt` be utilized' such as at the dotted position ofv the leads such as lilbetween stages2 and n, in orderto provide a desired pulse repetition frequency.

Referring'now to FIG. 2,..the operating characteristics of the avalanche transistors-utilized in the` circuits in accordance with this inventionwillbe further explained.

For the arrangement of the transistors-such as 2li whichV is essentially in a grounded emitter arrangement, the voltage V along the X-axis of lthegraph vof FIG. 2 represents the photential maintained at the collector of the transistor Ztl andthe current I Vof ,the Y-axis represents the current owing in the collector thereof. Becausethe transistor, 2,0 is essentially.grounded` through diode T11 when initiated into conduction, as will be explainedsubsequently,h,the avalanche operationmay beexplained with the groundedemitter characteristics-of F162. Asiswell known, the operatingy characteristics of an avalanche transistor may include a first region where a, which is the ratio,of collector to emittercurreut, is less thanl indicating that the current throughl the collector ofthe transis-V tor is less than through the emitter.` rThis'rst-region is below a voltage Vs at the collector ofthe transistor 20,

which is the voltage at which the Ibase current is internally compensated at thecollector by an avalanche multiplicationeffect or current multiplication between the4 collector and -the emitter so that a=l. When the collector is biased to a higher potential than Vs, whichisasecondregion of operation where is greater than l` avalanche multiplication causes more current to flow into.

the collector of the transistor than ilows into the emitter upto a breakdown volta-ge Vb. At this'breakdownvoltf age the multiplication'of collector to'v emitter current ,in an-p-n type transistor becomes essentially infinite.' The operating region between they collector voltages negative resistance region.

aand

l VVs and Vb, because of the avalanche multiplication effect, is av It is to be noted that the above avalanche emitter operation in the transistor 2i) is only initiated when the base to emitter junction is sufficiently forward biased so that electrons are able to travel into the base region. Thus, a standby condition is maintained in the transistor when a voltage V1 is applied to the collectors thereof and the base to emitter junction is forward biased a small amount. A. load line h6 during the standby period has a relatively small slope because the resistor i4 has a relatively large value. A standby point 93 at the voltage V1 is selected at the junction ofV the load line 96 andin the positive region of a characteristic negative resistance line 166.

v The voltage V1 of the standby point 9S is selected slightly emitterto the base path of the n-p-n type transistor 20 is forward biased a predetermined V'arnountyelectrons or carriers travel from the emitter to the collector thereof. Thecollector to base junction isa high'intensity field region because of the. bias maintained betweenthecollector; and emitter, Vand in response to the. electrons, produce holey Yelectron of thecrystal latticeand are also ionized. to produce additional electrons. 'Iheholes 4are .therrswept back to the base to `emitter junction and ou their wayfree more hole electron pairs to provide a regenerative feed-bachi this avalanche multiplication, thev currentthrough the collector ofthe transistor 2% is subf action. Because of stantially greater than through the emitter thereof.

pairs lay-,collision with the atoms below the breakdown voltage V13 so as to prevent steady state current Mico, whichis the avalanche multiplication factor times the steady state current, from becoming innite. Also, the voltage V1 is selected relatively close to the'voltage V1, so as Yto maintain a large potential dierencebetween the collector and emitter and the transistor 26, which potential difference causes thev area of accumulatedelectrons in the transistor to increase and'th'e rate of hole electron pair' production to increase when the base to emitter junction is forward biased.I The biastvoltage V1 maintained at the collector of the'tran'sistor 20 is equal to the potential at the positive source of potential 46 minus the voltage drop caused by the steady state 'cur rent Mico flowing through the resistor Thus, the 'resistor 44has a relatively. large value so' that the current MI5., is. maintained at a rninimumarnountto prevent eX- cessive power dissipation.

Now that the standbyY operating point 9S has been determined, the pulse forming operation in the negative resistance region ot the transistor Ztl will beV further explained. The potential VV1 at the'collector of the transistor 2@ is equal to the +200 volts at the source of potential 46 minus the voltage drop ofthe Mlc'ocurrent through emitter junction of the transistor'Z is forward vbiased an:

increased amount so that electrons are allowed topass into the base region to start the regenerative feedback action. The operating point of the transistor Ztl afterV the avalanche breakdown and multiplication is. initiated thus moves from the characteristic negative 'resistance' curve lili) along the load-line 96 to a characteristic. negative resistance curve such as l. When the trigger :pulse of the `waveform 76 is removed from the base of the transistor 2i), the operation may shift to another 'characteristic line such as 166. lt is to be noted that the operation of the transistor 20 after avalanche multiplication is. initiated is independent of the presenceof the trigger pulses of the waveform 79. Essentially,v a short circuit is present between the collector and emitter of the transistor Zlwith the avalanche multiplication resulting from the high field strength at the base to collector junction thereof i causing the current in the collector to bergreater than the current inthe emitter by the multiplication factorv M. However, substantially all of the current that flows into the collector of the transistorV 20 is obtained from the charge on the respective capacitors 36 and 42 which limitV the current to prevent thevtransistors from" being destroyed.- Y

While the capacitors 35 and 42. dischargeftheir stored charge through the transistorl 12,'the voltages at the lead 30 decrease to Vs and may discharge to ground potential because of the stored carriers in the base-region of the transistor. As the capacitors 36 and 42 discharge and the operation of the transistor Ztl moves along a negative resistance line such as 1%, transient load-lines similar to load-lines and 17121 are present inthe negative resistance region with' the lines generally moving to the left as the voltage on the collector decreases. Whenl the v voltage on the lead 30 is below Vs, the transistor 20 continues to conduct current because the transistor remains substantially forward biased between the base to emitter as a result of the internally stored carriers in that region. While the capacitors 36 and 42 are discharging current through the transistor 2G, a pulse of the waveform 14 is developed across the load 18 as a result of current liowing through the lead 1S and a pulse is developed on the lead 74 similar to the waveform 14. Shortly after the current sources of the capacitors 42 and 46 are completely discharged, the transistor 20 recovers internally when free carriers in the base region are recombined so that the reverse biased base to emitter junctions prevent further conduction. Also at this time, the capacitors 36 and 42 start to charge by current flowing from the source of potential 46 until after a relatively long time interval, the voltage V1 is again established on the leads 40 and 44 by the stored positive charges on the plates 34 and 40 of the capacitors 36 and 42. The sequential operation in accordance with this invention provides time for the capacitors 36 and 42 to be recharged to allow operation at a' high pulse repetition frequency because for satisfactory operation, the transistor 20 must be returned to the standby point 98 before the pulsing operation is repeated.

Referring now to the waveforms of FIG. 3, as well as to the circuit of FIG. l, the operation with tunnel diode logic to develop load pulses at a repetition rate substantially independent of the recovery time of the storage capacitors such as 36 and 42 will be further explained. It will be assumed for purposes of explanation that stage 1 has previously been set to the ready state as a result of stage n developing an output pulse of the waveform 14 in response to a trigger pulse of the waveform 13. In the ready state, the diode T11 is at a low voltage ready state B as shown on a characteristic negative resistance curve 116 of a graph 12) where the X-axis indicates negative voltage -V as a result of positive potential applied to the cathode'of diode T11 and the owing therethrough. The tunnel negative voltage thereat maintains state B.

ln all other stages such as stage 2 and stage n tunnel diodes T12 and T1n are at normal low voltage state C and tunnel diodes T22 and T2n are at a low voltage state B, which relatively small negative voltage maintains the diodes T12 and T1n at the normal state C.

Upon the application of a negative trigger signal 124 of the waveform 13, the diode T11 changes to a high voltage state A as a load line 123 rises above the peak of the curve 116. The large negative voltage across the diode T11 at state A combined with the negative voltage of t e pulse 124 cause the avalanche transistor 20 to be initiated into conduction so that current s-tarts to ow Vfrom the capacitors 36 and 42 through the collector to emitter path thereof. It is to be noted 4that other transistors such as 20a and 201: at state C are not changed to state B because the negative voltage of the pulse 124 is not by itself sucient to cause the diodes T12 and T1n to exceed the peak voltage of their characteristic curves 116:1 and 116i). Because the capacitors 36 and 42 are effectively a source of potential, a positive potential is applied to the cathode of T11 as current is conducted therethrough and diode T11 automatically changes from state A to the low current state C. Also, as the avalanche transistor conducts current, through diode T21, the positive potential applied to the cathode thereof changes diode T21 to the low voltage state B for maintaining the diode T11 at state C after termination of the conduction of the diode 29. Thus, stage l is returned to the normal state.

As the capacitor 48 discharges, Aan output pulse 128 of the waveform 14 is developed across the load 18 because current flows from ground through the load 18 to the negative plate 48 of the capacitor 36. As the control capacitor 42 simultaneously discharges through the collector to emitter path of the transistor 29, a negative diode T11 at the ready Y-axis indicates current diode T21 is at a high v voltage state A as shown by a graph 122 so that the large pulse is also developed on the lead 74 and applied through the lead 84 to the cathode of the diode T22. This negative potential developed between the cathode and anode of diode T22 sets ready state B. The negative potential developed across the ldiode T22 maintains the diode T12 at the ready state B at the termination of the negative pulse on the lead 84. Thus, the tunnel diode logic of stage 2 is in the ready state and the tunnel diode logic of stage 1 has been returned to the normal state. It is to be noted that the width of the trigger pulses of the waveform 13 must be suiciently narrow so as to be terminated before the diode T21 is changed to state B or the stage 2 will be energized. However, utilizing conventional semiconductor techniques, .the source 12 may develop pulses sufficiently narrow to be terminated during the inherent time delay before the diode T11 is set to the ready state B.

It is to be emphasized that the automatic reset operation of diode T11, for example, in accordance with this invention allows the transistor 20 to be triggered at the emitter while utilizing a minimum amount of power from the source 12. As discussed above, when the negative pulse is applied to the the avalanche transistor 20 is initiated into conduction from the positive source of the capacitors 36 and 42,

current passes in the reverse direction through diode T11, and that diode is automatically reset to the state C. 'l Thus, the transistor 20 conducts the major of the load current through a low impedance so that there is a'mimimum power loss of the load current during formation of the pulse 128 of the waveform 14. Therefore, the diode T11 has a high impedance state during triggering and,

automatically resets to a low impedance state after the transistor 29 is initiated into conduction. Although the diode T21 causes diode T11 to change to the ready state B response to the negative trigger signal 124, the capacitor 35, which in the normal state has a positive charge on the plate 4t) and a negative charge on the plate 48, begins to rapidly discharge. As a result, a large pulse of current flows from ground through the load 18 to the plate 48 forming the output pulse 128 of the waveform 52.

Because of the potential drop of the plate 48 of the cai pacitor 36 discharging through the transistor 20, the diode 52 is biased into a conductive state. Other diodes 'of the OR gate such as 52a and 52b are not rendered conductive as only the transistor Ztl of state 1 has been triggered into conduction. Oscillations at the termination of the pulse 128 are substantially suppressed by the presence of the diode 19 across the load 18. It is to be noted that because of the arrangement of the storage capacitor 36, the circuit presents a low output impedance to the load 18.

It is to be again noted that only in the ready stage such f V as stage 1 the tunnel diode 11 in the ready state B responds to the low amplitude trigger pulses of the waveform 70. The opera-ting point of diodes such as T12 and T111 at the normal state C rises on the characteristic curve 116 in response to the negative potential of the pulse 124 of the waveform 70, but the negative potential of the pulse 124 is insuiicient to change the diodes T12 and T1n to state A.

Now after the completion of the above operation to form the load pulse 128 with stage 1 having been returned diode T22 to state A and sets T12 to the cathode of diode T11 which is at l the ready state B, diode T11 is rapidly changed to the n high voltage state A so that a relatively small current is passed therethrough to ground from the source 12. When emacs-e to the normal state and stage 2 changed to the ready state, a second trigger pulse 132 applied to the lead 10 triggers the avalanche transistor 20a and a similar operaV tion as discussed above forms a pulse 131i as current flows .through the load 18 and the diode 52a to the discharging capacitor 36a. Also,the diode T12 is reset to the normal state C and the diode T22 is changed to the normal state B. In response to the negative pulse developed by the discharge of capacitor 42a', diode Tgn is set to the ready state A and diode T 1 is set to the ready state B. Thus, upon the occurrence of a trigger pulse 138, transistor Zlb of stage n is initiated into conduction and a load pulse 1412 is formed as capacitor 36 discharges through the collector to emitter path of the transistor Zlib. The diodes Tm and Tgn are respectively reset to the normal states C and B and diodes T11 and T21 in response toa'n'egative pulse on the lead Sb are respectively set .to states B and A so that stage l is in the ready state.

Thus, upon the occurrence of a trigger pulse 144, stage 1 again forms a load pulse i415 and vupon the occurrence of a trigger pulse 15), stage 2 forms'a load pulse 152, each stage being sequentially tired in accordancey with thisinvention'. Because'theftifneibetween firing any'particular stage is' rri'ultiplied by? n; the`number of stages utilized, recovery time is provided for the storageY capacitors and the repetition VVfrequency may be increased town' timesthe allowable frequencywhen utilizing a single stage. For example, `while a single stage is limited to approximately 1 rnc. repetition rate' by; the recovery timerthereof, three stages as shown in FIG. l'rn'ay operate at approximately a 3 `rnc. repetition rate'. It is to be noted that with'a plurality Vof stages repetitionfrequencies are only limited bythe width of the pulse whichv may be approximately 5 milli-rnicro-seconds The circuit'in accordance with this invention is operable at pulse repetition frequencies'up to 20G mc. by providing sufficient Voperating stages in accordance with the principles ot this'inventionf It is to be noted that the pulse-formingcircuit in accordance with this invention is not vlimited to n-p-n type transistors butp-n-p types may be utilized by reversing the polarities ofthe circuit in accordance with well known principles.

Thus, thereha-s been described a simplified power driver utili-zing avalanche transistor for developing relatively narrow pulses at a very high pulse reptitionfrequency. As a result ofy the utilization of tunnel diode logic, inductive elements are eliminated to provide a circuit that has a minimum weight and is highly applicable to printed circuit techniques. Because of the automatic reset operationl vof the tunnel diode coupled to the emitter of the avalanche transistor, a minimum power is utilized from the source of trigger pulses.

What is claimed is: v y

1. A pulse forming circuit comprising a source of trigger pulses, a load, a plurality of stages each including an avalanchetransistor having a first :andra second 'electrode and a base, biasing means coupled -to the base of said transistor, first and second sources of potential, a current limiting resistor coupled between said first source ofipo# tential and the first electrode of said-transistor, Ya r'st storage capacitor coupled between the first electrode and said load, a first tunnel diode coupled between the second electrode of said transistor potential, said source of trigger pulses coupled to the second electrode of said transistor, a second tunnel diode coupled between the second electrode of said transistor and said second source of potential, biasing means coupled to the second electrode of said-transistor, a second storage'capacitor coupled from theiirst electrode of said transistor 'to saidsecond tunnel diode, and means sequentially' and continuously coupling said second storage capacitor'of each stage to the second tunnel'diode of the succeeding -stage, whereby sequentially in each of Vsaid stages said first tunnel diode is set to a rst potential state and said second source ofV lto respond to a trigger pulse to form a load pulse and then reset to a second potential state so as to be unresponsive to a trigger pulse.

2. A pulse forming circuit comprising a source of trigger pulses, a load, a plurality of pulse forming stages each including first, second and third sources of potential, an avalanche transistor having' a base, an emitter and a collector, voltage divider means coupled between said first and second sources of potential and to said base, a current limiting resistor coupled between said third source of potential and said collector, a first charging capacitor having one plate coupled to said collector, a gating diode coupled between the other plate of said first charging capacitor and said load, means coupling said emitter to said source of trigger pulses, a first tunnel diode having a cathode and an anode coupled respectively between said emitter and said second source o f potential, a first resistor havingone end'coupled to said emitter, a second tunnel diode having an anode and a cathode with the cathode coupled to the other Vend of said rst resistor, a second resistor coupled between the anode of said second tunnel diode and said second source of potential, a second charging capacitor coupled between said collector and the anodeot said second tunnel diode, a third resistor coupled between the cathode of said second tunnel diode and said first' source ot potential, and connecting means coupled between the anode of said second tunnel diode of one stage said plurality of stages.

3. A pulse forming circuit including a plurality of stages.`

for responding to trigger pulses applied from a source to sequentially be rendered operative to apply a pulse through an OR gate'to a load comprising in each stage a transistor having avalanche characteristics with a base, a collector and an emitter, first, second and third'sources of potential, biasing means coupled to the first and secf ond sources of potential and to the base of said transistor, a currentV limiting resistor coupled between said third source of potential and the collector of said transistor, iirst storage means coupled between the collector vof said transistor and the OR gate, connecting means coupling the source of trigger pulses to the emitter of said transis-V tor, a first tunnel diode coupled between the emitter or athird vresistor coupled betweeri'the firstV end of said sec-` ond tunnel diode and said first source of potentiaL'and means sequentially-and continuously coupling the second endV of said 'second tunnel diode'in each stage to the first end -of said second tunnel diode in the succeeding stage whereby each'stage sequentially applies a pulse to said load'irrresponse to succeeding Vtrigger pulses.

4. A` circuit for applying pulses to a load at a high repetition rate'in response' to a'source of trigger pulses comprisingV a plurality of'pulse forming stages each including a'tran'sistor operating in the avalanche mode and having a base and a first and second electrode, biasing means coupledY to said base, a source of power coupled to said first electrode, a first storage capacitor having a first platefcoupled to the first electrode and a second plate coupled to the load, means coupling the Ysecond electrode to the 'source of trigger pulses, a source of reference potential, a first negative resistance device coupled between said emitter and said source 'of reference potential and having a low voltage state, an 'intermediate voltagestate and a high voltagelstate, a second negative resistance device coupled between said emitter and said source of reference potential and having a low voltage state and a high voltage state, a second storage capacitor coupled between said first electrode and said second negative resistance device, and interconnecting means coupled between the second storage capacitor of each stage to the second negative resistance device of the succeeding stage so that all of said plurality of stages are continually and sequentially coupled, whereby only one of said stages is in a ready state with said iirst device at the intermediate voltage state and said second device at the high voltage state and all other stages are in the normal state with said first device at ti e low voltage state and the second device at the low voltage state, said stage at a ready state responding te a tri ger pulse so that said iirst device changes to the high voltage state and in turn to the low voltage state and said second device changes to the low Voltage state and in the succeeding stage said first device changes to the intermediate voltage state and said second device changes to the high voltage stage so that only a succeeding stage responds to each succeeding trigger pulse to apply a pulse to said load.

5. A logical element for controlling a current conductive device having a first terminal coupled to a rst source of potential and having a second terminal, the device being responsive to an initiating signal applied to said second terminal to be initiated into conduction, the logical element responding to a pulse from a tirst source of pulses to be set from a normal state to a ready state and responding to a trigger pulse from a second source of pulses when in the ready state to provide the initiating signal to the second terminal, the logical circuit returning to the normal state after being initiated into conduction comprising second and third sources of potential, a irst tunnel diode coupled between the second terminal of the device and the second source of potential, a first resistor having one end coupled to the second terminal of said device, a second tunnel diode having a rst and a second end with the tirst end coupled both to the other end of said first resistor and to the rst source of pulses, a second resistor coupled between the second end of said second tunnel diode and said second source of potential, storage means having a iirst end coupled to the irst terminal of said device and a second end coupled to the second end of said second tunnel diode, a third resistor coupled between the rst end of said second tunnel diode and said third source of potential and means coupling the second terminal of said device to said second source of pulses.

6. A circuit operable when set from a normal state to a ready state in response to a pulse from a rst source to respond to a trigger pulse applied from a second source to develop a pulse across a load comprising a transistor having avalanche characteristics with a base, a collector and an emitter, lirst, second and third sources of potential, biasing means coupled to the tirst and second sources of potential and to the base of said transistor, a current limiting resistor coupled between said third source of potential and the collector of said transistor, tirst storage means coupled between the collector of said transistor and the load, irst connecting means coupling the second source of pulses to the emitter of said transistor, a first tunnel diode coupled between the emitter of said transistor and said second source of potential, a rst resistor having one end coupled to the emitter of said transistor, a second tunnel diode having a tirst and a second end with the iirst end coupled to the other end of said iirst resistor, a second resistor coupled between the second end of said second tunnel diode and said second source of potential, second storage means having a first end coupled to the collector of said transistor and a second end coupled to the second end of said second tunnel diode, a third resistor coupled between the rst end of said second tunnel diode and said first source of potential, and second connecting means coupling the rst source of pulses to the iirst end of said second tunnel diode, whereby when said iirst and second tunnel diodes are set in the ready state, the circuit responds to a trigger pulse to apply a pulse to said load and to be reset to the normal state.

References Cited in the tile of this patent UNITED STATES PATENTS 2,594,336 Mohr Apr. 29, 1952 2,838,664 Wolfendale June 10, 1958 2,958,046 Watters Oct. 25, 1960 OTHER REFERENCES 1960 International Solid-State Circuits Conference, February 10, 1960 (iirst edition), Esaki (Tunnel) -Diode Logic Circuits, Nett et al., pages 16, 17. 

1. A PULSE FORMING CIRCUIT COMPRISING A SOURCE OF TRIGGER PULSES, A LOAD, A PLURALITY OF STAGES EACH INCLUDING AN AVALANCHE TRANSISTOR HAVING A FIRST AND A SECOND ELECTRODE AND A BASE, BIASING MEANS COUPLED TO THE BASE OF SAID TRANSISTOR, FIRST AND SECOND SOURCES OF POTENTIAL, A CURRENT LIMITING RESISTOR COUPLED BETWEEN SAID FIRST SOURCE OF POTENTIAL AND THE FIRST ELECTRODE OF SAID TRANSISTOR, A FIRST STORAGE CAPACITOR COUPLED BETWEEN THE FIRST ELECTRODE AND SAID LOAD, A FIRST TUNNEL DIODE COUPLED BETWEEN THE SECOND ELECTRODE OF SAID TRANSISTOR AND SAID SECOND SOURCE OF POTENTIAL, SAID SOURCE OF TRIGGER PULSES COUPLED TO THE SECOND ELECTRODE OF SAID TRANSISTOR, A SECOND TUNNEL DIODE COUPLED BETWEEN THE SECOND ELECTRODE OF SAID TRANSISTOR AND SAID SECOND SOURCE OF POTENTIAL, BIASING MEANS COUPLED 